Bleach is commonly used to whiten soiled fabrics during laundry operations. The most common bleach is aqueous sodium hypochlorite referred to as chlorine bleach. Chlorine bleach is effective and cheap but has certain disadvantages. It cannot be mixed with the detergent in a single package. It tends to attack certain dyes and also degrades fabrics. In addition, fabrics having a resin finish (wash and wear fabrics) are given a noticeable yellow tint by chlorine bleach.
In order to overcome these disadvantages, another class of laundry bleach has come into use. This class is referred to as peroxygen bleach. These materials are very effective whitening agents and are much safer with dyed fabrics. In addition they do not yellow wash and wear fabrics. Many can be packaged together with a detergent and other components to form a single detergent-bleach laundry package.
Although peroxygen bleaches have these many attributes, they have several drawbacks. They are more expensive compared to chlorine bleach and also are not effective unless the wash solution is at a temperature high enough to activate the peroxygen compound. For example, sodium perborate requires a water temperature above about 160.degree. F. which is higher than that usually attained in domestic (U.S.A.) laundry operations. In order to lower the temperature at which peroxygen bleach can be used, one alternative is to use "bleach activators". These are compounds that by themselves have no bleaching action but when used in combination with a peroxygen bleach form a peroxygen compound which is more effective at lower temperatures than the initial peroxygen bleach. Examples of such bleach activators are tetraacetylethylenediamine, sodium p-acetoxybenzene sulfonate and sodium p-heptanoyloxybenzene sulfonate.
It has also been reported that in certain metal cations, in particular manganese (II), are excellent activators for peroxygen bleaching agents such as sodium percarbonate and sodium perborate. They are most effective when used in combination with a compound that releases carbonate anions into the aqueous wash solution (Oakes, U.S. Pat. No. 4,481,129).
More recently it has been reported (Namnath, U.S. Pat. No. 4,536,183) that use of soluble manganese (II) cations as bleach activators can stain the fabric due to the oxidation of the manganese to a higher valence state. The presence of a strong oxidizing agent in the laundry wash solution (such as sodium hypochlorite) can oxidize the Mn(II) to Mn(IV) which can adhere to the fabric causing it to take on a brownish appearance. Namnath solved this problem by incorporating the Mn(II) cation into a solid silicon support (e.g. zeolite) which prevents the manganese from depositing on the fabric.
Namnath prepares the silicon supported manganese bleach activator by
(a) dissolving a water soluble manganese (II) salt and a solid silicon support in a solvent; PA0 (b) adjusting the pH to achieve a value from 7.0 to 11.1; PA0 (c) separating the solid composition; PA0 (d) washing the solid composition to remove any traces of free manganese (II) salts; and PA0 (e) drying the solid composition to remove solvent and moisture.
Alternatively, the solid silicon support material can be placed in a water solution of the manganese (II) salt to absorb the manganese cations and the resulting slurry of the solid manganese exchanged silicon support spray dried. The zeolite supported manganese (II) is shown by Namnath to be a very effective activator for perborate bleach.